• 대한인간공학회지
• /
• 제33권6호
• /
• pp.565-575
• /
• 2014

Objective: The aim of this study is to evaluate the effect of weight of load and time on the physical workload of repetitive upper-limb tasks with handling light weight loads using EMG and perceived discomfort, and to investigate the relationship between EMG and perceived discomfort for those repetitive tasks of moving light weight loads. Background: Repetitive upper-limb motion is known as one of the main risk factors of musculoskeletal disorders, and a lot of repetitive tasks are carried out while handling light weight loads in the industry. In evaluating the workload of repetitive tasks handling light weight loads, EMG and perceived discomfort can be used, though their relationship in those work conditions are not much investigated. Method: A laboratory experiment with 18 healthy males were conducted to record EMG signals from 5 muscle sites of the right arm and shoulder and rate perceived discomforts for the body parts and the whole body while carrying out repetitive materials-handling tasks for 52min. The subjects were divided into 3 groups which handled the loads of 1kg, 2kg and 3kg, respectively. ANOVAs were conducted to analyze the effects of the weight and time on RMS of EMG amplitude (normalized RMS: NRMS), median frequency of power spectrum of EMG (normalized MDF: NMDF) and perceived discomfort. The correlations between NRMS and NMDF and perceived discomfort were also analyzed. Results: Statistically significant muscular fatigue effects were not found from NRMS and NMDF in most muscles, while there were significant increases of discomfort as the task time elapsed. It was shown that there were an increasing trend of the muscular activity as the weight of load increased and a decreasing trend of median frequency of EMG of upper and lower arms as time elapsed. It was found that there were significant negative correlations between NMDFs from the lower arm and discomfort ratings, though the relationships were weak. Conclusion: It can be concluded that the working conditions adopted in this study were not enough to induce muscular fatigue, while there was significant increase in perceived discomfort. A further study is necessary to integrate the objective and subjective measures for more reliable and sensitive evaluation of workload of repetitive tasks of handling light weight loads. Application: This study can be used as a basic study for the evaluation of workload of repetitive tasks handling light weight loads.

• 대한인간공학회지
• /
• 제26권4호
• /
• pp.153-160
• /
• 2007

Due to the high occurrence rate of musculoskeletal disorders(MSDs), many Korean companies adopted various assessment tools to evaluate workers' musculoskeletal stress. Using the results of this evaluation, tasks were selected for improvements. However, there are still many workers who complained of musculoskeletal stress of their tasks. Their tasks usually consist of repetitive activities and a short rest cycle. This prompts a concern of reliability of the evaluation tools and especially RULA. Thus in this study, OCRA(The Occupational Repetitive Action tool) was used to check whether RULA(Rapid Upper Limb Assessment) evaluates workers' musculoskeletal stress reasonably well since OCRA has been known to be a good evaluation tool for repetitive tasks and tasks with short recovery periods. The evaluation was conducted on 142 tasks. It was found that 65 tasks showed higher action levels by OCRA than by RULA. However, 13 tasks showed the reversed result and 64 tasks showed the same level regardless of the evaluation tool. It was concluded that either RULA or OCRA alone cannot evaluate all types of tasks very well. It is suggested that OCRA needs to be used with RULA together for the evaluations of musculoskeletal stress at workplaces where repetitive activities and short recovery periods exist.

• 한국산업보건학회지
• /
• 제16권2호
• /
• pp.81-90
• /
• 2006

The Strain Index(SI) has been commonly used to evaluate the musculoskeletal disorders(MSDs) of upper extremities. Recently, the American Conference of Governmental Industrial Hygienists(ACGIH) adopted the Threshold Limit Value for hand activity level (HAL TLV) focused on the hand, wrist, and forearm. The MSDs risks of 37 repetitive works conducted at an automobile climate control system manufacturing factory were evaluated using both the HAL TLV and the SI, and the results by two methods were compared. Also, measured repetitive frequencies of upper limbs joint were mesured using electromyogram and electrogoniometer. The evaluation results of the HAL were related with the repetitive frequency data of upper limbs joint by electrogoniometer, and the NPF was related with %MVC of ECU. The evaluation result of HAL TLV was highly related with the SI score(r=0.66, p<0.01). Of total 37 tasks, 25 tasks(67.6%) were exceeded the TLV and 34 tasks(91.9%) exceeded the SI limit. Although there was a high relationship between the HAL TLV and SI score, the HAL TLV underestimated the risk in comparison with the SI. The correlation coefficients(r) between the HAL TLV data and the repetitive frequency of upper limbs joint were 0.45~0.55(p<0.01). The MSD symptoms was significantly different between high risk groups and low risk groups evaluated by HAL TLV(p<0.01), but was not different between two groups by SI. In conclusion, the HAL TLV is a proper tool for repetitive works.

• 대한조선학회 특별논문집
• /
• 대한조선학회 2017년도 특별논문집
• /
• pp.28-31
• /
• 2017

The independent tank surface create formation consists of repetitive tasks, but this study deletes the existing manual and repetitive tasks and facilitate the create formation of tank surface.

• 대한산업공학회지
• /
• 제23권1호
• /
• pp.1-22
• /
• 1997

Learning control refers to controllers that learn to improve their performance at executing a given task, based on experience performing this specific task. In a previous work, the authors presented a theory of indirect decentralized learning control based on use of indirect adaptive control concepts employing simultaneous identification and control. This paper extends these results to apply to the indirect repetitive control problem in which a periodic (i.e., repetitive) command is given to a control system. Decentralized indirect repetitive control algorithms are presented that have guaranteed convergence to zero tracking error under very general conditions. The original motivation of the repetitive control and learning control fields was learning in robots doing repetitive tasks such as on an assembly line. This paper starts with decentralized discrete time systems, and progresses to the robot application, modeling the robot as a time varying linear system in the neighborhood of the desired trajectory. Decentralized repetitive control is natural for this application because the feedback control for link rotations is normally implemented in a decentralized manner, treating each link as if it is independent of the other links.

• 대한의용생체공학회:의공학회지
• /
• 제28권1호
• /
• pp.139-147
• /
• 2007

The aim of this study was to evaluate effects of short-tenn repetitive-bilateral excercise on the activation of motor network using functional magnetic resonance imaging (fMRI). The training program was performed at 1 hr/day, 5 days/week during 6 weeks. Fugl-Meyer Assessments (FMA) were performed every two weeks during the training. We compared cerebral and cerebellar cortical activations in two different tasks before and after the training program: (1) the only unaffected hand movement (Task 1); and (2) passive movements of affected hand by the active movement of unaffected hand (Task 2). fMRI was performed at 3T with wrist flexion-extension movement at 1 Hz during the motor tasks. All patients showed significant improvements of FMA scores in their paretic limbs after training. fMRI studies in Task 1 showed that cortical activations decreased in ipsilateral sensorimotor cortex but increased in contralateral sensorimotor cortex and ipsilateral cerebellum. Task 2 showed cortical reorganizations in bilateral sensorimotor cortex, premotor area, supplemetary motor area and cerebellum. Therefore, this study demonstrated that plastic changes of motor network occurred as a neural basis of the improvement subsequent to repetitive-bilateral excercise using the symmetrical upper-limb ann motion trainer.

• 대한인간공학회:학술대회논문집
• /
• 대한인간공학회 1997년도 추계학술대회논문집
• /
• pp.433-436
• /
• 1997

Automobile assembly tasks consist of many kinds of manual work which are very stressful to workers because of repetitive poor working postures and dealing heavy weights. To decrease the level of workload, it is necessary to evaluate the workload quantitatively. In this study, a workload evaluation method based on EMG was experimentally evaluated. We measured EMG at 6 main muscles with 2 healthy male workers during doing 9 assembly tasks, which were selected as high workload jobs. The tasks were decomposed into 36 elementary tasks. The workload was calculated through an equation with %MVIS and work duration time. To evaluate the result, subjective discomfort on the tasks was assessed by 29 workers. By the calculated workload, we were able to ranked the workload of tasks, elementary tasks. The comparison between the EMG-based workload and subjective rating showed a positive correlation(P-value=0.0246). We think it is possible to adapt the EMG-based workload evaluation technique to all assembly tasks by expending the experi- ment size.

• 한국멀티미디어학회논문지
• /
• 제22권4호
• /
• pp.432-442
• /
• 2019

Most current human action recognition methods based on deep learning methods. It is required, however, a very high computational cost. In this paper, we propose an action change detection method to reduce repetitive human action recognition tasks. In reality, simple actions are often repeated and it is time consuming process to apply high cost action recognition methods on repeated actions. The proposed method decides whether action has changed. The action recognition is executed only when it has detected action change. The action change detection process is as follows. First, extract the number of non-zero pixel from motion history image and generate one-dimensional time-series data. Second, detecting action change by comparison of difference between current time trend and local extremum of time-series data and threshold. Experiments on the proposed method achieved 89% balanced accuracy on action change data and 61% reduced action recognition repetition.

• 한국안전학회지
• /
• 제23권5호
• /
• pp.119-124
• /
• 2008

Many automobile assembly workers often do several cycles of tasks continuously, i.e., without breaks, to get a longer break. This is not recommended since the dose of fatigue increases exponetially with time and it takes much longer time to recover. In this study, a laboratory experiment was conducted to investigate the effect of work/rest schedules on workload of a repetitive upper-limb task. Eleven male subjects participated in the experiment, in which simulated screw driving tasks were carried out repetitively with 3 different work/rest schedules: standard breaks(1 cycle of work at a time, 60 20-s breaks), medium breaks(5 cycles of work at a time, 12 100-s breaks), and long breaks(10 cycles of work at a time, 6 200-s breaks). The result showed that medium- and long-breaks schedules significantly increased the level of perceived discomfort and %HRR as compared to the standard-break schedule. The subjects' preference was not statistically different among work/rest schedules, which might be caused from the absolutely low level of workload of the experimental tasks. From the results, it is recommended to have frequent and shorter breaks rather than infrequent and longer breaks to decrease the level of physical workload. A more expanded studies, however, should be carried out to provide more practical safety guidelines on the work practice of continuous working without breaks among automobile assembly workers.

• 한국산업정보학회논문지
• /
• 제9권4호
• /
• pp.56-67
• /
• 2004

본 연구는 단순반복작업을 실시하고 있는 작업자(본사, 하청회사)들을 대상으로 Human Error(인간실수)의 실태를 분석하고, 예방대책을 마련하고자 486명을 대상으로 진행되는데 연구결과를 요약하면 다음과 같다. 먼저 Human Error(인간실수)가 가장 많이 발생하는 요인으로서 작업자 요인이 $77.8\%$로 가장 많고, 기계적 요인이 $16.3\%$, 관리적 요인이 $6.0\%$순으로 나타나 Human Error(인간실수)는 주로 단순반복 작업을 수행하는 작업자에 의해 발생하는 것으로 볼 때 기계적 오류에 의한 발생제거보다 작업자들의 자세와 신체적 결함, 장시간 지속작업 등에 기인한 것을 의미한다. 그리고 Human Error(인간실수)가 가장 많이 발생하는 인간정보처리 계통의 에러 요인에서는 동작조작에러가 $46.9\%$로 가장 많았고, 판단기억에러가 $36.4\%$, 인지확인에러가 $16.7\%$순으로 나타나 단순동작의 반복으로 인해 조작과정에서의 에러가 가장 많이 발생하고 있는 것으로 분석되었다. 이상에서 볼 때 전체적으로 자동화의 실행으로 Human Error(인간실수)가 줄어들 것이라는 일반적인 관념을 깨고 아직도 반복적인 단순 반복 작업 공정에서 각 공정이나 기능간 기기보다 작업자의 순간적 오류가 지속적으로 발생하고 있는 현실에서 각 공정에 따른 경력별 순환 보직이나 교환근무 등을 통한 업무 표준화와 능률개선을 위한 현장 점검제 등으로 보다 적극적인 회사차원에서의 지속적인 설비개선과 예산 지원이 요구된다.